The quality of crude oil throughout the world is reduced by acidic components found in the oil. During refining, at temperatures between 220 and 400° C., these species can become corrosive. Organic acid species commonly referred to as naphthenic acids, having boiling points in this temperature range will condense on metal surfaces leading to damage in the refinery infrastructure, potential safety issues, and costly repairs. As a result, oils with high acid content, whether from conventional (crude oil) or oil sands (bitumen) sources, are more difficult to market and their value is significantly discounted.
Total acid number (TAN) is an analysis that tends to correlate with the corrosive nature of oils. Most refineries will minimize their exposure to oils with TAN values greater than 0.5 mg potassium hydroxide (KOH) per gram of oil. Some newer refineries have improved their front-end metallurgy so that they can handle TAN values up to 1.0 mg KOH/g. However, bitumens and heavy crude oils can have TAN values greater than 2.0 mg KOH/g.
Organic acids contribute significantly to the corrosion problems in refineries (Meredith et al. in Organic Geochemistry, 2000, 31, 1059-1073). In Alberta, Athabasca oil sands contain significant amounts of organic acids that are problematic not only to the refineries that receive the bitumen, but contribute to the toxicity of the waters used during bitumen extraction (Holowenko et al. in Water Research, 2002, 36, 2843-2855; and Rogers et al. in Chemosphere, 2002, 48, 519-527). The Canadian Oil Sands Network for Research and Development (CONRAD) Upgrading Research Group has identified that high total acid number (TAN) values, a number that reflects the corrosive nature of crude oil, pose a major concern to the industry that are processing Alberta bitumens and heavy crudes.
Conventional methods to remove corrosive species from crude oil involve costly and energy-intensive chemical and thermal processes. For example, the current technologies developed to remove organic acids from crude oil involve either thermal decomposition at 400° C. (Blum et al. in U.S. Pat. No. 5,820,750), adsorbing onto inert materials (Varadaraj in U.S. Pat. No. 6,454,936), treating with surfactants (Gorbaty et al. in Canadian Patent 2,226,750) or converting the organic acids into various derivatives that are easier to remove (Brons in U.S. Pat. No. 5,871,637, Sartori et al. in Canadian Patents 2,343,769 and 2,345,271, and Varadaraj et al. in U.S. Pat. No. 6,096,196).
Efforts to minimize organic acid corrosion have included a number of approaches for neutralizing and removing the acids from the oil. For example, there are numerous approaches in the literature on the reduction of the organic acid species in crude oil. They include thermal decomposition of organic acids using high temperatures in the presence (U.S. Pat. Nos. 5,914,030, 5,928,502) or absence (U.S. Pat. No. 5,820,750) of a metal catalyst and treatment of corrosive acids with group IA and IIA metal oxides, hydroxides and hydrates to form metal salts of naphthenic acids which are then thermally decomposed at elevated temperatures (U.S. Pat. Nos. 5,985,137, 5,891,325, 5,871,637, 6,022,494, 6,190,541, 6,679,987). Other methods include chemical formation of esters of the organic acids in the presence of alcohol and a base (U.S. Pat. Nos. 5,948,238, 6,251,305, 6,767,452, and Canadian Patent 2,343,769), reducing acidity by the formation of various salts of organic acids using base (U.S. Pat. Nos. 5,643,439, 5,683,626, 5,961,821, 6,030,523), removal of naphthenic acids using detergents or surfactants (U.S. Pat. Nos. 6,054,042, 6,454,936), absorbing organic acids onto polymeric amines (U.S. Pat. Nos. 6,121,411, 6,281,328) and by adding corrosion inhibitors to crude oil to prevent naphthenic acid induced metal corrosion (U.S. Pat. No. 5,552,085).
While these processes have achieved varying degrees of success, most of these methods are costly and energy-intensive and their effectiveness somewhat limited. As a result, there is a need to develop alternative approaches to treat and eliminate organic acid species in petroleum.
An alternative to utilizing energy intensive thermal, physical or chemical methods may be a biological approach using enzymes that have the capability to remove or convert the acidic carboxyl groups from organic acids into products that are not corrosive.
The art is substantially bereft of methods for upgrading the quality of crude oil comprising organic and/or naphthenic acids by the use of enzymes or biocatalysts. U.S. Pat. Nos. 7,101,410, 6,461,859 and 5,358,870 describe the use of biocatalysts, such as bacteria, fungi, yeast, and algae, hemoprotein, and a cell-free enzyme preparation from Rhodococcus sp. ATCC 53969, respectively, to improve the quality of oil specifically target organic sulphur containing molecules and so reduce the sulphur content as well as lowering their viscosity. U.S. Pat. No. 5,858,766 describes the use of microorganisms (a bacteria strain) in a bioupgrading capacity to selectively convert organic nitrogen and sulphur molecule in oil as well as remove metals.
It has been reported that Micrococcus luteus (formerly Sarcina lutea) ATCC 533 can convert fatty acids into long chain hydrocarbons via a decarboxylation-condensation mechanism (Albro et al. in Biochemistry, 1969, 8, 394-405, 953-959, 1913-1918 and 3317-3324). The organism is now known as Kocuria rhizophilia and has similar characteristics to a closely related organism M. luteus. This microorganism is one of a group of microorganisms and plants that possess enzymes that may be useful in a bioupgrading process that can biosynthesize hydrocarbons from carboxylic acids. The organisms and plants are described in a series of review articles (Hackett L. P. in Microb. Biotechnol. 2008, 1, 211-225; Ladygina, et al. in Proc, Biochem. 2006, 41, 1001-1014; Khan et al. in Biochem. Biophys. Res. Comm. 1974, 61 1379-1386; and Kolattukudy et al. in Biochem. Biophys. Res. Comm. 1972, 47, 1306-1313).
There remain the needs for bioprocesses, as attractive alternatives to current upgrading methods, which use microorganisms (biocatalysts), or catalysts derived from these organisms (enzymes), to improve the quality of crude oil and bitumen by converting organic acidic species.